JP2002065719A - Cornea operation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cornea operation device capable of performing an operation properly by improving correcting precision by the removal of a cornea. SOLUTION: The cornea operation device for removing the cornea by laser beams is provided with an arithmetic means for calculating the removing quantity of the cornea based on the ametropia of an eye to be examined and dividing the removing quantity into the steps of plural times for obtaining the removing quantities at the respective steps, a controlling data deciding means for deciding the controlling data of the device at the respective steps based on the respective removing quantity, a cornea shape measuring means having an image forming optical system for forming an index for measuring the shape of the cornea on the cornea, an image pickup optical system for picking up the index image formed on the cornea and a shape arithmetic means for processing the picked-up image to detect the index image to obtain the shape of the cornea, and a correction means which compares an actually removing quantity at the step with a planed removing schedule based on the shape of the cornea measured after finishing irradiation with laser at a step by using the cornea shape measuring means and correcting controlling data at the next step based on the comparison.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corneal surgery apparatus for ablating (ablating) a cornea of a patient's eye with a laser beam to correct the refractive of the patient's eye.

[0002]

2. Description of the Related Art There is known a laser corneal surgery apparatus in which a cornea of a patient's eye is excised using an excimer laser and the refractive power of the cornea is changed to correct refractive errors such as myopia, hyperopia, and astigmatism.
In this refractive surgery, PRK surgery (photorefractive keratectomy) in which laser irradiation is performed after the corneal epithelium is peeled off
LASIK surgery (laser as), in which a layer from the corneal epithelium to the parenchyma is incised in layers to form a flap, and then the parenchyma is excised by laser irradiation and the flap is returned again.
sisted in-situ keratomileusis).

[0003] In addition, in refraction correction using this type of device,
An ablation amount is set from data related to refraction correction such as a corneal shape, a corrective refractive power, and a size of an optical region before the operation stage, and laser irradiation is performed based on the ablation amount. For measuring the corneal shape, a device that measures the corneal shape by projecting a placido ring onto the cornea and detecting specularly reflected light from the cornea is generally used.This measuring device is separated from the surgical device. It is a thing.

[0004]

However, in the measurement of the corneal shape using specular reflected light, the corneal shape measurement immediately before the laser irradiation (P
In RK, after removing the corneal epithelium, in LASIK, after forming a flap), and the shape immediately after laser irradiation cannot be measured, and it is known whether or not the cornea has been ablated according to the set ablation amount. I couldn't do that. For this reason,
Conventionally, the refraction is measured before and after the operation to judge the appropriateness of the operation, and if the desired correction has not been made, the operation is performed again after the patient's eye is recovered. This is burdensome for the patient.

The present invention has been made in view of the above-mentioned problems of the prior art,
It is an object of the present invention to provide a corneal surgery apparatus capable of improving correction accuracy by corneal ablation and performing a more appropriate operation.

[0006]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) In a corneal surgery apparatus for ablating a cornea by a laser beam, an ablation amount of the cornea is calculated based on a refractive error of the eye to be examined, and the ablation amount is divided into a plurality of steps to perform ablation in each step. Calculating means for calculating the amount, control data determining means for determining control data of the apparatus in each step based on each ablation amount, an imaging optical system for forming an index for measuring a corneal shape on the cornea, and forming on the cornea A corneal shape measuring means having an imaging optical system for picking up the obtained target image, a shape calculating means for processing the picked-up image and detecting the target image to obtain a shape of the cornea; Correction means for comparing the actual ablation amount in the step with the planned ablation amount based on the corneal shape measured after the laser irradiation in the certain step, and correcting the control data in the next step based on the comparison. It is characterized by having.

(2) In the corneal surgery apparatus of (1),
The index for measuring the corneal shape is an index based on slit light, and the corneal shape measuring means is a means for moving the imaging optical system in a distance direction with respect to the cornea in predetermined steps, and is formed on the cornea at each moving position. The image forming apparatus further includes a unit that captures an image of the slit index using the imaging optical system.

(3) In the corneal surgery apparatus of (1),
The index for measuring the corneal shape is a lattice pattern.

(4) In the corneal surgery apparatus of (1),
The imaging optical system is also used as an alignment optical system for aligning a distance direction of the apparatus with respect to the cornea.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an external view of a corneal surgery apparatus that performs a corneal refractive correction using a laser beam.

Reference numeral 1 denotes a main body of a surgical apparatus, which includes an excimer laser light source and the like. Laser light from the excimer laser light source passes through a laser irradiation optical system in the main body 1 described later, and is guided to the arm 2. The inside of the arm portion 2 has an optical path of a laser beam, and an optical element such as a mirror is arranged. A binocular microscope unit 3 for observing a patient's eye, an illumination unit 4, and the like are provided at an arm tip 5 of the arm unit 2.

As shown in FIG. 2, the arm 2 is moved in the direction of FIG. 1 (left and right directions with respect to the operator) by an X-direction arm drive unit 51 and in the Y direction (with respect to the operator) by a Y-direction drive unit 52. (In the front-back direction). Also, the arm tip 5
Can be moved in the Z direction (vertical direction) by the Z-direction tip drive section 53. Each of the drive units 51, 52, 53 is composed of a motor and a slide mechanism.

Reference numeral 6 denotes a controller which controls the arm 2 to X
A joystick 7 for giving a signal for driving in the Y direction, a focus adjustment switch 6a for performing alignment in the Z direction, and a switch 6 for starting measurement of the corneal shape
b. Reference numeral 8 denotes a foot switch for transmitting a laser irradiation signal, and 9 denotes a computer for inputting various data of necessary surgical conditions and calculating, displaying, and storing laser irradiation control data. The computer 9 has a main body 9
0, a monitor 91, a keyboard 92, a mouse 93, and the like.

A schematic configuration of an optical system and a control system of the surgical apparatus main body 1 will be described with reference to FIG. A laser light source 10 emits an excimer laser having a wavelength of 193 nm.
The laser beam emitted in the horizontal direction from the laser light source 10 is reflected by mirrors 11 and 12 and
At 90 degrees. The plane mirror 13 can be moved in the direction of the arrow in the figure by the mirror driving unit 14, and the laser beam can be moved in parallel in the Gaussian distribution direction to uniformly cut the object. This point is described in Japanese Patent Laid-Open No.
No. 42644, which is described in detail.

Reference numeral 15 denotes an image rotator, which is driven to rotate about the central optical axis by an image rotator driving unit 16, and rotates the laser beam around the optical axis.
17 is a mirror.

Reference numeral 18 denotes a variable circular aperture for limiting the ablation area to a circular shape. The aperture diameter of the aperture is changed by an aperture driving unit 19. Reference numeral 20 denotes a variable slit aperture that limits the ablation region to a slit shape. The aperture width and the direction of the slit opening can be changed by an aperture driving unit 21. 22 and 23 are mirrors for changing the direction of the beam. Reference numeral 24 denotes a projection lens for projecting the circular aperture 18 and the slit aperture 20 onto the cornea Ec of the patient's eye.

Reference numeral 25 denotes a dichroic mirror having a characteristic of reflecting a 193 nm excimer laser beam and transmitting visible light. The laser beam having passed through the projection lens 24 is deflected by 90 ° by the dichroic mirror 25, and becomes a cornea E.
The light is guided to c.

Above the dichroic mirror 25, a fixation lamp 26, an objective lens 27, and a microscope section 3 are arranged. 3
Reference numeral 0 denotes a mirror disposed between the binocular optical paths of the microscope unit 3, and an imaging lens 31, a mirror 32, and a CCD camera 33 are disposed on the reflection-side optical path of the mirror 30. The output of the CCD camera 33 is connected to an image analyzer 34, and the corneal shape analysis result is input to the computer 9.

Below the dichroic mirror 25, slit projection optical systems 40a, 40
b are arranged symmetrically with respect to the optical axis of the objective lens 27. These slit projection optical systems 40a and 40b
In addition to being used as a projection optical system for alignment light, it is also used as a measurement optical system for projecting an index for measuring a corneal shape. Each of the slit projection optical systems 40a and 40b includes illumination lamps 41a and 41b that emit visible light, a condenser lens 4
2a, 42b, slit plate 43a having a cross slit,
43b and projection lenses 44a and 44b. The slit plates 43a and 43b may be slits of other shapes instead of the cross slits. The slit plates 43a and 43b are in a positional relationship conjugate with the cornea Ec with respect to the projection lenses 44a and 44b.
An image is always formed at a focus position on the optical axis of the camera. Also, the imaging surface of the CCD camera 33 is
And the focus position on the optical axis of the objective lens 27 is conjugated with the CCD camera 33. The CCD camera 33 is used as a slit projection image detection optical system.

Reference numeral 50 denotes a control unit for controlling the laser light source 10 and each drive unit. The computer 9, the foot switch 8, and the controller 6 are connected to the control unit 50.

Although not shown in the embodiment, the apparatus has an eye tracking function (a function of tracking the movement of a patient's eye and aligning the laser irradiation position when the patient's eye moves during alignment or laser irradiation). It is preferable to mount it. For this, the one described in Japanese Patent Application Laid-Open No. 9-149914 by the present applicant can be used.

Next, the operation of the device according to the present invention will be described. Here, a description will be given assuming that spherical correction of myopia is performed.

First, operating conditions such as the correction refractive power and the size of the resection area are input to the computer 9. Computer 9
Calculates corneal ablation amount data based on the input data. In addition, when performing the PRK operation, the surgeon performs a procedure in which the corneal epithelium of the patient's eye is peeled off before laser irradiation.

The operator operates the joystick 7 to move the arm 2 while observing the anterior eye image of the patient's eye with the microscope 3 so that the reticle (not shown) and the pupil have a predetermined relationship. Alignment in the X and Y directions is performed, and the focus adjustment switch 6a is operated to move the arm tip 5 up and down to perform alignment in the Z direction.

The alignment in the Z direction is performed as follows while observing the slit images projected by the slit projection optical systems 40a and 40b. Most of the slit light from the slit projection optical system 40a on the left side in FIG. 3 passes through the cornea Ec, but a part of the slit light is scattered by the cornea Ec and passes through the microscope unit 3 to form an arc in FIG. Is observed as the slit line 71a. The right slit projection optical system 40b
Similarly, the slit light from is observed as an arc-shaped slit line 71b in FIG. Reference numeral 72 denotes a cross line orthogonal to the center of the slit lines 71a and 71b. Now, if the vertex of the cornea Ec is at the focus position of the microscope unit 3, the slit line 71a from the left and the slit line 71b from the right overlap at the cornea vertex position as shown in FIG. However, when the cornea Ec is farther from the focus position, as shown in FIG.
1a and 71b appear apart. When the cornea Ec is on the upper side of FIG. 2, that is, on the near side, as shown in FIG.
The book slit lines 71a and 71b appear to intersect.
Therefore, when it looks like FIG. 4B, the arm tip 5 is lowered, and when it looks like FIG. 4C, on the contrary, the arm tip 5 is raised. In this way, by adjusting the distance between the apparatus and the cornea Ec so as to obtain the state shown in FIG. 4A, the microscope unit 3 can be focused on the cornea Ec.

When the alignment is completed, the switch 6b of the controller 6 is pressed to measure the corneal shape before laser irradiation. Preferably, the apparatus detects the state of FIG. 4A and automatically starts measurement. The slit lines 71a and 71b formed on the cornea are imaged by the CCD camera 33, and the image is input to the image analysis unit. Further, the arm tip 5
Are sequentially moved upward and downward by a predetermined amount based on the alignment position, and an image captured by the CCD camera 33 is input to the image analysis unit 34 for each movement.

Slit line 71 formed on cornea
The method of measuring the corneal shape using a and 71b will be described. Now, it is assumed that the slits from the slit projection optical systems 40a and 40b are projected on a flat plate. When the flat plate is at the reference height position (focus position), as shown in FIG.
The slit lines 71a and 71b coincide with each other on the central axis Lo. When the flat plate is below the reference height position, as shown in FIG. 5B, two slit lines 71a,
71b is away from the central axis Lo. At this time, the distances Qa, Q of the respective slit lines 71a, 71b from the center axis line
b changes in proportion to the height difference from the reference height position in the height direction.

When this slit is projected onto a substantially spherical cornea, its shape becomes a curve as shown in FIG. In FIG. 6, if the interval Qx between the central axis Lo and the inner edge of the slit line 71a is sequentially detected, corneal height information at many points on the slit line 71a formed at this time can be obtained. If the slit projection position with respect to the cornea is raised or lowered, the coordinate positions of the slit lines 71a and 71b change as shown in FIGS. 4B and 4C, so that the height at each point on the cornea is changed. Information can be obtained. In this calculation, the amount of movement of the arm tip 5 for raising and lowering the slit projection position is corrected.

After the slit image is analyzed by the image analysis unit 34 using such a principle, the computer 9 determines the corneal shape from the corneal height information of each coordinate. Note that the captured image includes a slit image scattered by the iris, but is distinguished by image processing based on a difference in the positional relationship with the slit image scattered by the cornea, brightness, and the like.

After measuring the corneal shape, the foot switch 8 is pressed to perform laser irradiation. In myopia correction, the laser beam is limited by the circular aperture 18 and the plane mirror 13 is sequentially moved to move the laser beam in the Gaussian distribution direction. Then, each time the laser beam moves on one surface (one scan), the moving direction of the laser beam is changed by rotation of the image rotator 15 (for example, 12
In three directions at 0-degree intervals), a region limited by the circular aperture 18 is ablated substantially uniformly. By performing this every time the size of the opening diameter of the circular aperture 18 is sequentially changed, myopia correction that increases the radius of curvature of the cornea can be performed (see Japanese Patent Application Laid-Open No. 6-114083).

Here, the apparatus of the present embodiment is programmed to perform laser irradiation in two stages. For example, the first laser irradiation is set to perform 70% of the total planned excision amount (correction amount). When the first laser irradiation is completed, after performing alignment, the switch 6b is pressed, and the corneal shape is measured in the same manner as described above. When the computer 9 obtains the corneal shape after the laser irradiation, the computer 9 subtracts the corneal shape after the laser irradiation from the corneal shape before the laser irradiation to obtain the actual ablation amount (actual ablation amount) by the first laser irradiation. Then, the planned ablation amount to be set in the second laser irradiation is calculated based on the comparison between the scheduled ablation amount and the actual ablation amount in the first laser irradiation. The control data of the second laser irradiation is corrected based on this data.

The calculation of the scheduled ablation amount in the second laser irradiation will be described. The total planned ablation amount is St, the planned ablation amount at the first laser irradiation is S1, and the actual ablation amount is S1.
′, The ablation error ratio K by the first laser irradiation
Is represented by K = S1 ′ / S1.

The amount to be ablated by the second laser irradiation is St-S1 '. If an error occurs at the same ablation error ratio K in the second laser irradiation, the amount to be ablated will be set to the second time. The ablation amount Sx is as follows: Sx = (St−S1 ′) / K

After the expected ablation amount Sx in the second laser irradiation is obtained in this manner, when the foot switch 8 is pressed again, the computer 9 outputs corrected control data for ablating the expected ablation amount Sx. It is sent to the control unit 50, and the control unit 50 controls the laser light source 10 and each driving unit. The laser irradiation is controlled by a method of controlling the opening diameter of the circular aperture 18 by converting the expected ablation amount Sx into a refractive power. Alternatively, it is also possible to examine the excision depth of each point from the planned excision amount Sx and control it by the opening diameter of the circular aperture 18. Since the second laser irradiation takes into account the error of the first laser irradiation, it is possible to perform an operation closer to the set total planned excision amount.

After the second laser irradiation, the alignment is performed again, and the corneal shape is measured by the same method as described above. By displaying the result on the monitor 91, it is possible to confirm the quality of the operation. Here, if the resection amount (correction amount) is insufficient, the laser irradiation may be continuously performed.

In the above corrective surgery, laser irradiation may be divided into more than two stages, in which case the corneal shape is measured after laser irradiation at a certain stage,
The laser irradiation control data at the next stage is corrected in the same manner as described above.

The correction of myopia has been described above, but correction of astigmatism and correction of hyperopia can be performed in the same way.

Although PRK has been described above, in the case of LASIK surgery, the corneal shape before and after laser irradiation after the flap is stripped can be measured in the same manner as described above and fed back to the next laser irradiation.

The corneal shape measuring optical system in the above embodiment is provided with a mechanism for rotating the slit projection optical systems 40a and 40b around the optical axis of the objective lens 27, and sequentially changes the slit projection angle in predetermined steps. The entire shape of the cornea may be measured by taking a slit image while taking the image.

Further, the corneal shape measuring optical system may be provided exclusively without being used also as the projection optical systems 40a and 40b for the alignment light, and may be as follows. In FIG. 7, reference numeral 100 denotes an index projection optical system; 101, an index plate on which a fine lattice pattern (including a dot-like lattice pattern) is formed;
And the projection lens 103 forms an image of a lattice pattern at a focus position on the optical axis of the objective lens 27. The index detection CCD camera 105 is arranged on an optical axis symmetrical to the index projection optical system 100 with the optical axis of the objective lens 27 interposed therebetween, and takes an image of a lattice pattern projected on the cornea.
The image analyzer 34 measures the corneal shape by detecting a change in the distance between the lattice patterns captured by the CCD camera 105. With such a measurement optical system, the entire surface of the cornea can be measured from one captured image. Also, in order to prevent the slit light for alignment not shown from becoming noise, the illumination lamps 41a and 41b of the slit projection optical systems 40a and 40b are turned off during measurement. Alternatively, the illumination light source 10
2 may be an infrared light source, and a filter for cutting visible light may be provided in front of the CCD camera 105 to detect a lattice pattern using infrared light.

[0042]

As described above, according to the present invention,
Correction accuracy by corneal resection can be improved, and surgery can be performed more appropriately.

[Brief description of the drawings]

FIG. 1 is an external view of a corneal surgery apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a mechanism of an X- and Y-direction arm drive unit and a Z-direction tip drive unit.

FIG. 3 is a schematic diagram of an optical system and a control system of a corneal surgery apparatus according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a slit line in an alignment state.

FIG. 5 is a diagram illustrating a slit line projected on a flat plate.

FIG. 6 is a diagram illustrating a slit line projected on the cornea.

FIG. 7 is a schematic view showing another example of a corneal shape measuring optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Surgery apparatus main body 3 Microscope part 9 Computer 33 CCD camera 34 Image analysis part 40a, 40b Slit projection optical system 50 Control part 53 Z-direction tip drive part 71a, 71b Slit line 100 Index projection optical system 105 CCD camera

Claims (4)

[Claims] In a corneal surgery apparatus for ablating a cornea by a laser beam, an ablation amount of a cornea is calculated based on a refractive error of an eye to be examined, and the ablation amount is divided into a plurality of steps, and the ablation amount in each step is calculated. Calculating means for determining the control data of the apparatus at each step based on each ablation amount; an imaging optical system for forming an index for measuring a corneal shape on the cornea; A corneal shape measuring means having an imaging optical system for picking up the target image, a shape calculating means for processing the picked-up image and detecting the target image to obtain the shape of the cornea, and using the corneal shape measuring means. Correction means for comparing the actual ablation amount in the step with the planned ablation amount based on the corneal shape measured after the laser irradiation in the step, and correcting the control data in the next step based on the comparison A corneal surgery device, characterized in that: 2. The corneal surgery apparatus according to claim 1, wherein the index for measuring the corneal shape is an index based on slit light,
The corneal shape measuring means includes means for moving the imaging optical system in a distance direction with respect to the cornea at predetermined steps, and means for imaging the slit index formed on the cornea at each movement position by the imaging optical system. Characterized corneal surgery device. 3. The corneal surgery apparatus according to claim 1, wherein the corneal shape measurement index is a grid pattern. 4. The corneal surgery apparatus according to claim 1, wherein the imaging optical system is also used as an alignment optical system for aligning a distance direction of the apparatus with respect to the cornea.